Ballast for light system

ABSTRACT

A ballast for fluorescent lamps is disclosed. The ballast of this invention will function at two different frequencies and will provide the same, or if desired, different light intensity when power is supplied at the different frequencies.

United States Patent Sarbacher et al.

[ NOV. 18, 1975 BALLAST FOR LIGHT SYSTEM 3.018.410 1/1962 Cornell 315/1510. 5

. 3. 2 i 3 5 [75] Inventors: Robert I. Sarbacher, Manna Del 195 7/1965 Femberg et I no) M Ray; Robert E. Mauch, Los Angeles, both of Cahf' Primary Examiner-Michael J. Lynch [73] Assignee: John C. Bogue, Santa Monica, Calif. Assl'mm Davis Attorney, Agent, or FirmW1therspoon and Lane [22] Filed: Aug. 8, 1973 [21] Appl. No.: 386,584

[57] ABSTRACT [52] US. Cl. 315/141; 3l5/DIG. 5; 315/284 [51] h lt. Cl. H06B 17/00 A ballast for fluorescent lamps is disclosed. The bal- Flew 0f 'c G- 258, last of this invention will function at two different fre- 315/284 quencies and will provide the same, or if desired, different light intensity when power is supplied at the dif- [56] Ref rences C t d ferent frequencies.

UNITED STATES PATENTS 2.765,428 10/1956 Campbell 315/258 7 Claims, 1 Drawing Figure 2| 24 2;: l8 i l6 US. Patent Nov. 18, 1975 3,921,033

BALLAST FOR LIGHT SYSTEM BACKGROUND OF THE INVENTION This invention relates to fluorescent lamp ballasts, and more particularly to fluorescent lamp ballasts which will function at two different frequencies.

Fluorescent lamps are in general normally powered by the standard commercial utility power which in the l US. is generated at a frequency of 60 hertz. The ballasts used with such lamps are designed to function at this frequency. If the lamps are to be powered from a source having a frequency other than the standard 60 hertz, ballasts designed to operate at the frequency of that power source must be used. Thus, a given fluorescent lamp system cannot be operated at different power source frequencies with a single ballast. The ballasts available on the market today are designed for single frequency operation. These ballasts are, of course, not generally sharply tuned and will operate satisfactorily within a limited frequency band on either side of their design frequency. However, these present day ballasts are designed to operate on a single frequency only and will not operate if the frequency of the available power source is substantially different than the design frequency of the ballasts.

As long as the fluorescent lamps are to be operated from but a single power source or from power sources all having the same frequency, the single frequency characteristic of the presently available ballasts present no problem. If, on the other hand, the lamps are to operate from power sources having different frequencies, the ballasts would have to be changed each time the power source was changed. Under certain conditions or circumstances it may be desirable or even necessary to operate fluorescent lamps from a power source other than the normal utility power, and in such cases it is often advantageous to generate the power at a frequency different than the frequency of the utility power supply. Prior to this invention, the ballasts would have to be changed when switching from the utility power supply and then changed back to the 60 hertz ballasts when switching back to the utility power supply. This, of course, is cumbersome and under certain circumstances is so totally unacceptable that the generated power supply out of necessity has to operate at the 60 hertz frequency of the utility power supply. There may also be circumstances under which a given fluorescent lamp system may be operated from two different power sources, neither of which has a frequency of 60 hertz. Using presently available ballasts, this would also, of course, require separate sets of ballasts for each of the power supplies.

This invention provides a ballast that will operate at two different frequencies. Thus, with the ballast of this invention, a given fluorescent lamp system can be operated from two power sources having different frequencies. To those skilled in the art, many different applications for such ballasts will come to mind. For example, such ballasts can be used in emergency lighting systems where the frequency of the locally generated emergency power supply is different than 60 hertz; in systems designed to meet specialized lighting requirements such as stroboscopic effect reduction; in low noise systems; in high efficiency systems; and in many other systems where two different frequency power sources are either available, desirable or necessary.

SUMMARY OF THE INVENTION This invention provides a fluorescent lamp ballast which will function at two different frequencies and will provide the same or. if desired, a different light intensity when power is supplied at two different frequencies.

A conventional rapid-start ballast is configurated to operate as a magnetically shunted autotransformer 0 comprised of two windings wound on a core. The magnetic shunt element of the ballast provides very loose coupling between the windings of the autotransformer. This prevents the flux linkage from the primary winding of the autotransformer from driving excessive current through the secondary winding independent of the voltage developed across the secondary winding by the primary flux.

Capacitors are normally connected in the secondary winding of the autotransformer. The values of the capacitors and the shunt element are chosen to provide the proper operating current to the lamps at the design frequency. Thus, the ballast provides the proper current to the lamps, but at the same time provides the current limiting which is necessary for the operation of the fluorescent lamps. This holds true only at the design frequency.

At higher frequencies, the effect of the magnetic shunt element increases so as to reduce the maximum flow coupling from the primary winding to the secondary winding of the autotransformer. Thus, the current generated in the secondary winding that is available to the lamps is reduced. This reduction of current will either render the lamps inoperative or operate the lamps with a low light intensity depending upon the frequency of the power source relative to the design frequency.

This decrease in flux and resultant reduction in current is compensated for in this invention by the addition to the conventional ballast of a capacitor and a pair of windings designed to provide the additional flux at the higher frequency. The additional windings and the additional capacitor modify the character of the transformer such that a proper amount of current is applied to the lamps at both the higher and lower frequencies. In fact, by selecting the proper value for the additional capacitor and the proper value for the additional windings, the ballast can be modified to supply the same amount of current to the lamps at the high frequency as is supplied at the lower frequency. Of course, the values of the additional windings and the capacitor can be chosen to select either more or less current at the higher frequency than is supplied at the lower frequency. Thus, the ballasts of this invention provide for the operation of fluorescent lamps at two different frequencies.

BRIEF DESCRIPTION OF THE DRAWING The exact nature and the structural details of the invention can be readily understood from the following detailed description of the invention when read in conjunction with the annexed drawing in which the single FIGURE shows a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION In the drawing, the fluorescent lamps are illustrated by the rectangular boxes 16 and 17. The filaments of the lamps are not shown. A ballast 26, designed in accordance with this invention, is electrically connected to the lamps l6 and 17. Power to the lamp system is applied at the terminals 24.

The capacitors 18 and 19, the windings 11 and 14, and the core 10 are shown arranged in the normal or conventional configuration for a rapid-start ballast. These elements form a conventional type of rapid-start ballast available on the market today. Core 10 is provided with a pair of magnetic shunt elements 20. Windings 11 and 14, and shunt elements operate as a magnetically shunted autotransformer comprising windings 11 and 14. Thus, the flux linkage from winding 11 is prevented from driving excessive amounts of current through winding 14 independent of the voltage developed across secondary winding 14 by the primary flux. The current which flows in secondary winding 14 is delivered to lamps l6 and 17 through capacitors l8 and 19. At the given design frequency of ballast 26, the values of capacitors 18 and 19 and shunt elements 20 are so chosen or adjusted to provide the proper operating current to lamps l6 and 17; while at the same time, as described above. the ballast provides the current limiting necessary for the operation of the lamps at the design frequency.

The values of the components thus far described can be chosen to provide. within practical limits, proper operation of lamps l6 and 17 at any single frequency. In the U.S., fluorescent lamps are generally supplied with power from the conventional 60 hertz commercial utility supply. Thus, the values of windings l1 and 14, shunt elements 20 and capacitors 18 and 19 are chosen to provide the proper current to lamps l6 and 17 at 60 hertz.

If the lamps l6 and 17 are operated from a power source having a frequency higher than the design frequency of the ballast comprising windings 11 and 14, shunt elements 20, core 10, and capacitors 18 and 19, the effect of the shunt elements 20 increases in such a manner as to reduce the flux coupling from primary winding 11 to secondary winding 14. This reduction in flux coupling results in a decrease of the current generated in winding 14; and therefore, a decrease in the current available to fluorescent lamps 16 and 17. This reduction in current will cause lamps 16 and 17 to operate at a reduced light intensity or the lamps may not light at all, depending on how great a reduction in current has taken place. Thus, lamps l6 and 17 will not operate or will not operate satisfactorily except with power sources having a frequency that matches the design frequency of ballast elements thus far described.

The decrease in flux and resultant decrease in current available to lamps 16 and 17 at higher frequencies is compensated for in ballast 26 by the addition of the windings l2 and 13 on core 10 and the addition of capacitor 15, as shown in the FIGURE. The addition of windings l2 and 13 and capacitor 15 provides additional flux linkage at the higher frequency. Capacitor 15 provides the necessary coupling for high frequency operation but has little or no effect at the lower frequency of operation since it offers a high impedance at the lower frequency.

By selecting the correct value for capacitor 15 and the correct values for windings l2 and 13, ballast 26 can be so designed that it will deliver the same amount of current to lamps l6 and 17 at both the high and low frequencies. Of course, the value of the components can be so selected that different amounts of current can be supplied at the two frequencies.

While not absolutely essential, the inductor 21 may be added as shown to aid in the equalization of lamp brilliance when the lamps are operated at the higher frequency. Inductor 21 prevents capacitor 18 from partially shunting lamp 17 when operating at the higher frequency. In addition, the choke 22 may be added, if desired, to obtain better coupling at the higher frequency.

From the foregoing description, it is apparent that this invention provides ballasts for fluorescent lamps that will operate the lamps from power sources having different frequencies. Ballast 26 is essentially a conventional ballast so modified that fluorescent lamps can be operated either from a power source having a given frequency and from a power source having a frequency higher than the aforesaid given frequency. Thus, ballast 26 increases the flexibility of fluorescent lamp systems and renders such lamp systems readily and conveniently useable in many different applications for which heretofore the use of fluorescent lamp systems has been either too cumbersome or totally unsatisfactory.

While the invention has been described with reference to a preferred embodiment, it will be apparent to those skilled in the art that various modifications and changes can be made to the preferred embodiment without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A ballast for fluorescent lamps comprising:

first means for supplying proper fluorescent lamp operating current at a given frequency, said first means including a transformer core member, a magnetic shunt integral with said core member, first and second windings wound on said core in such a manner that said first and second windings form an autotransformer having a primary winding and a secondary winding, and first and second capacitors coupled to said secondary winding; and second means operatively associated with said first means for so modifying the operation of said first means that said first means is capable of also providing a proper fluorescent lamp operating current at a frequency higher than said given frequency.

2. A ballast as defined in claim 1 wherein said second means comprises a third and fourth winding wound on said core in series and a third capacitor connected in series with said third and fourth windings.

3. A ballast as defined in claim 2 wherein said first and second capacitors each have one side coupled to a common point of said secondary winding.

4. A ballast as defined in claim 2 wherein said first capacitor is directly coupled to said secondary winding and said second capacitor is coupled to said secondary winding through an inductor.

5. A ballast as defined in claim 2 wherein a choke is connected in series with said third and fourth winding and said third capacitor.

6. A ballast as defined in claim 4 wherein a choke is connected in series with said third and fourth winding and said third capacitor.

7. A ballast system for fluorescent lamps comprising:

ballast means having an autotransformer, said autotransformer having a primary winding and a secondary winding, said ballast means providing proper fluorescent lamp operating current at a given frequency, and

modifying means operatively associated with said ballast means for increasing the flux linkage becurrent at a frequency higher than said given frequency. 

1. A ballast for fluorescent lamps comprising: first means for supplying proper fluorescent lamp operating current at a given frequency, said first means including a transformer core member, a magnetic shunt integral with said core member, first and second windings wound on said core in such a manner that said first and second windings form an autotransformer having a primary winding and a secondary winding, and first and second capacitors coupled to said secondary winding; and second means operatively associated with said first means for so modifying the operation of said first means that said first means is capable of also providing a proper fluorescent lamp operating current at a frequency higher than said given frequency.
 2. A ballast as defined in claim 1 wherein said second means comprises a third and fourth winding wound on said core in series and a third capacitor connected in series with said third and fourth windings.
 3. A ballast as defined in claim 2 wherein said first and second capacitors each have one side coupled to a common point of said secondary winding.
 4. A ballast as defined in claim 2 wherein said first capacitor is directly coupled to said secondary winding and said second capacitor is coupled to said secondary winding through an inductor.
 5. A ballast as defined in claim 2 wherein a choke is connected in series with said third and fourth winding and said third capacitor.
 6. A ballast as defined in claim 4 wherein a choke is connected in series with said third and fourth winding and said third capacitor.
 7. A ballast system for fluorescent lamps comprising: ballast means having an autotransformer, said autotransformer having a primary winding and a secondary winding, said ballast means providing proper fluorescent lamp operating current at a given frequency, and modifying means operatively associated with said ballast means for increasing the flux linkage between said primary winding and said secondary winding thereby so modifying the operation of said ballast means that said ballast means is capable of also providing proper fluorescent lamp operating current at a frequency higher than said given frequency. 